Premixed Charge Compression Ignition (PCCI) is a known process for fueling a diesel engine in a manner that creates an air-fuel charge inside an engine cylinder during a compression upstroke of a piston during an engine cycle. After a desired quantity of fuel for the charge has been injected into the cylinder, the increasing compression of the charge by the upstroking piston creates sufficiently large pressure to cause auto-ignition of the charge as the piston is coming to top dead center (TDC). Auto-ignition may occur as the substantially simultaneous spontaneous combustion of vaporized fuel at various locations within the mixture.
While PCCI is known to provide certain advantages for limiting the creation of certain constituents in products of in-cylinder combustion that affect tailpipe emissions, PCCI is limited to use at relatively lighter engine loads and relatively lower engine speeds. For relatively heavier engine loads and relatively higher engine speeds, conventional diesel (CD) combustion is used. The nature of CD combustion inherently generates soot that remains in the products of combustion exhausted from the engine cylinders. In order to reduce the amount of soot in tailpipe emissions, some engine exhaust systems include diesel particulate filters for trapping soot. The trapped soot is burned off either naturally as the engine operates (natural regeneration) or by increasing exhaust temperature through the burning of extra fuel (forced regeneration). The burning of extra fuel reduces fuel economy of a vehicle that is being driven by such as engine.
Processor-controlled fuel injection systems having high-pressure fuel injectors, such as HEUI injectors, are capable of controlling fuel injection with precision that allows fuel to be injected at various injection pressures, at various times, and for various different durations during an engine cycle. Certain fuel injectors have been shown capable of developing injection pressures as high as 3,300 to 3,600 bar. It is anticipated that even higher maximum pressures will be achieved as further development continues.